Operation of internal combustion engine systems inherently produces audible sound. In many environments, engine noise is considered objectionable, particularly at certain frequencies and intensities. The multitude of moving parts and combustion explosions attendant to engine operation tend to generate noise in a frequency range and at intensities which can be annoying to operators and bystanders in the general vicinity of an engine. In recent years, certain jurisdictions have enacted regulations specifically directed to reducing noise associated with engine systems and other machines.
Engineers have long used a variety of means to block, absorb and/or redirect noise generated by operation of internal combustion engine systems. In the context of mobile machines such as trucks and construction machines, it is well known to place sound absorbing panels in various positions about an engine compartment such that noise generated during operation of the engine system is prevented from travelling outwardly to the extent practicable. A variety of materials and assemblies specifically directed to blocking engine sound from escaping to ambient have been proposed.
United States Patent Application Publication No. 2006/0103171 to Blomeling et al. is directed to one type of sound suppressing panel system for positioning about engine system components. In particular, Blomeling et al. (“Blomeling”) propose a sound insulation strategy using an underbody covering with a sound-absorbing part covered with a micro-perforated, heat shielding layer. In one version of Blomeling's design, the micro-perforated layer is exposed toward an underbody of a motor vehicle in the vicinity of parts of an exhaust train. Thus, in Blomeling sound would apparently travel from the inside of a motor vehicle through a micro-perforated layer and then be absorbed within the sound-absorbing part rather than escaping to the ambient environment. The disclosure, however, does not provide a suitable strategy for addressing noise issues where the vehicle structure is not amenable to the extensive use of sound suppression panels, or the use of such panels is insufficient to meet noise regulations.
There are obvious limitations to the extent to which an engine system, vehicle, etc. may be successfully isolated from ambient with sound suppression panels. On the one hand, if weight, size and hardware mounting issues did not exist, then any vehicle or engine system could be shielded from emitting noxious noise to the environment simply by adding additional sound suppression panels. Certain machine and engine system configurations, however, can limit the extent to which sound suppression panels may be positioned within and/or about an engine compartment. Expected future changes in engine emissions requirements have required certain new components to be added to some types of engine systems, or existing components such as particulate filters to be increased in size. Such components may be positioned inside an engine compartment and occupy space that was formerly available for positioning sound suppression panels. In addition, some newer engine operating strategies have come into common practice which increase the cooling demands on the engine cooling system, increasing the need to provide venting for the engine system and still further limiting the use of sound suppression panels about the engine compartment. While certain engine systems may be vented through a hood of the machine, this approach works poorly in the dusty and debris-laden environments often encountered by construction machines. Engineers have thus turned to placing vents in side panels of a machine body to permit some heat energy to escape. An undesired consequence of this approach, however, is the transmission of additional sound outwardly from the engine system. There is thus a multiplicity of concerns driving the search for improved means of suppressing engine system noise.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.